Calculation purpose and formula
Required attempts = good units ÷ (1 − failure rate). Required printer-hours = required attempts ÷ parts per cycle × cycle time. Required printers = ceiling(required printer-hours ÷ capacity per printer).
Interpret the result
Run this before committing to a date or deciding whether a temporary compatible printer is needed. The result rounds up because a fraction of a printer cannot cover a deadline.
Worked example
For 120 good units, four parts per six-hour cycle, five 16-hour days, 90% availability, 80% utilization, and no expected failures, the workload is 180 printer-hours. One printer supplies 57.6 productive hours, so four are required.
Assumptions and limitations
All counted printers can run the part and the work can be divided among them without a setup bottleneck. A calculated count does not reserve material, labor, finishing capacity, or shipping time.
Common planning mistake
Do not use planned units as attempts when failures matter; the schedule needs enough attempted cycles to create the required good units.